1. Field of the Invention
The present invention relates to a technology of an optical packet switching system used in an optical communication network.
2. Description of the Related Art
In optical communication networks, aiming for establishment of next-generation multimedia networks, an optical communication device of high speed and large capacity has been required. To realize a system providing high speed and large capacity, research and development of an optical packet switching system using a high-speed optical switch which can switch an optical path in a time on the order of nanoseconds (ns) has been advanced.
FIG. 1 is a diagram illustrating the optical packet switching system. An access node 14 such as a subscriber terminal or the like is connected to an edge node 11 via an access network. The edge node 11 is equipped with an optical packet assembly which coverts signal data from a subscriber into an optical packet. In addition, the edge node 11 is also connected to a core node 12. The core node 12 transmits an optical packet transmitted from the edge node 11 to a different core node 12 or an edge node 11 connected thereto.
Hereinafter, the core node 12 will be described with reference to FIG. 2. The core node 12 has a function of a matrix optical switch 21 for switching an optical path. The optical packet is transmitted by an optical data channel constituted by an optical fiber. The optical data channel is a channel utilizing a different wavelength than the optical fiber 13 physically connecting the edge node 11 and the core node 12. The wavelength of the optical packet is converted in the wavelength converting section 22. The optical packet whose wavelength has been converted is input into a matrix optical switch 21 and the pathway thereof is switched. The switch of the pathway in the matrix optical switch 21 is performed by a channel control section 24 and a reservation manager 23 controlling the matrix optical switch 21 by an instruction supplied by the channel control section 24 of a control section 25. Pathway information of the optical packet is input into the channel control section 24 of the control section 25 from a control channel. The channel control section 24 analyzes a label signal transferred via the control channel. The control channel may be a channel utilizing a different wavelength than that of the optical data channel in the optical fiber 13 physically connecting the core nodes 12 and may be an optical fiber or a coaxial wire which are different from the optical fiber 13. The reservation manager 23 analyzes the pathway information of the label signal transmitted via the control channel to control the matrix optical switch 21. The matrix optical switch 21 switches the pathway toward an output port instructed by the reservation manager 23.
FIG. 3 shows a switch timing at which the pathway is switched for transmittance of an optical packet 34. As shown in FIG. 3, the switch timing at which the pathway is switched for transmittance of the optical packet 34 is applied after a predetermined offset time 31 from application of a label signal 33 containing pathway information of the channel control section 24. The matrix optical switch is required to be switched for a short time, for example, the switch time 32 thereof is about 45 ns. This is a guard time imposed so as not to influence transmission of the optical packet 34. That is, an optical port must be switched within a short guard time in the optical packet switching system. Various investigations have been made into the matrix optical switch so as to enable the core node to be constituted. However, a structure with which switch of the optical port at a speed which satisfies the condition described above is performed has not been investigated. An example of a matrix optical switch for constituting a core node has been described in Japanese Laid-Open Patent No. 2003-21795.